The cleaning of contaminants from workpieces is an important step in many manufacturing processes. Unfortunately, many processes employ environmentally undesirable solvents, or are high temperature processes that are energy intensive. For example, vapor degreasing techniques employ both volatile organic solvents and high temperatures. Efforts to replace such processes with aqueous systems are not entirely satisfactory because of the problem of contacting water to substrates that may be oxidized thereby, and by the problem of cleaning the contaminated water. In addition, the drying of aqueous systems is very energy intensive.
Vegetable oils such as soybean oil and modified soybean oil have been suggested for cleaning, but have not received significant use because of either their high cost or the difficulty in removing or extracting residual components of the oil.
CO.sub.2 -based cleaning methods have been suggested. Some employ supercritical CO.sub.2, which (due to the need to handle higher temperatures and/or pressures) increases the cost of the apparatus used to carry out the processes. U.S. Pat. No. 5,377,705 to Smith et al. describes a precision cleaning system in which a variety of different co-solvents may be included (see column 8, lines 19-24 therein), with the mixture of the carbon dioxide and the co-solvent being either homogenous or heterogenous (see column 6, lines 4-11 therein). A problem with this system that it still does not provide a means to separate the contaminant from the co-solvent (see column 7, lines 24-32).
Accordingly, an object of the present invention is to provide a carbon-dioxide based cleaning system incorporating a separate cleaner, in which the contaminants may be separated from the cleaner to facilitate subsequent re-use or disposal of the cleaner.
A second object of the invention is to provide oil-based separation systems in which the oil, such as a vegetable oil, may be recovered for subsequent reuse.